Autoimmune diseases occur when the body's immune defenses overcome the normal tolerance mechanisms and attack the body's cells, organs and systems. Autoimmune diseases may be caused by an exogenous factor, or may arise spontaneously. Autoimmune diseases include a broad range of conditions that may be organ-specific or general. Among the organ-specific autoimmune disorders are rheumatoid arthritis and pemphigoid. Among the general autoimmune disorders are system lupus erythematosus and graft-versus-host disease (“GVHD”).
A number of autoimmune disorders produce oral symptoms. These include oral lupus, oral lichen planus [12], pemphigus vulgaris [24], oral aphthous stomatitis [14], pemphigoid [25], and GVHD [1,2,3]. In addition, there are immune consequences associated with acquired immune deficiency syndrome (AIDS), such as mucosal lichenoid changes and aphthae. These diseases are characterized by aberrant infiltration and activation by cells of the immune system, and exhibit various oral symptoms, including mucous membrane lesions, blisters, and erosions.
Oral lichen planus is a relatively common disease that can result in severe or chronic lesions involving mucosal surfaces, including the mouth [28]. These lesions can be very painful and persistent, lasting on the order of years. Oral lichen planus is often self-limiting; however, where treatment is required, systemic or intra-lesional steroid treatments are helpful. Topical steroids are only partially effective, and can lead to significant side-effects.
Pemphigus vulgaris is a mucocutaneous disease that often involves oral lesions. The distinctive symptom is blistering between certain layers of the epidermis. The blisters may be very painful and, if left untreated, may result in sepsis, cachexia, and major fluid and electrolyte imbalances reminiscent of those seen in severe burn patients [28]. Current treatment involves high doses of systemic corticosteroids and/or immunosuppressants, and because of the side-effects associated with these drugs hospitalization is often necessary.
Pemphigoid is divided into two forms—bullous pemphigoid and cicatricial pemphigoid. Of the two, cicatricial pemphigoid far more often involves oral lesions than bullous pemphigoid. Oral lesions are common in cicatricial pemphigoid, occurring in approximately 90% of cases [25]. Chronic mucosal lesions often lead to scarring, and ocular lesions may lead to blindness [28]. Treatment requires high levels of systemic corticosteroids and immunosuppressants, but even when given over long periods of time such treatments may be only partially effective.
Oral aphthous ulceration (“canker sores”) is a condition characterized by inflammatory lesions that occur principally in the mouth, although it can affect any mucosal surface. Although the cause is unknown, it has been postulated that that an autoimmune antigen-antibody reaction occurs [14]. Present treatment includes oral anaesthetics, improved hygiene and occasionally oral suspensions of tetracyclines and systemic and/or topical steroids [28].
Bone marrow transplantation (“BMT”) is a common treatment for many hematologic malignancies and immune deficiency states. BMT is used with increasing frequency for salvage therapy of many solid malignancies. Between 12,000 and 15,000 bone marrow transplants are performed each year in the United States. Of these, the number of allogeneic (donor) transplantations is estimated to be between 5,500 and 7,500. GVHD is a major complication of allogeneic BMT, occurring in 25% to 70% of BMT patients, despite GVHD prophylaxis [1].
GVHD occurs when genetically disparate but immunologically active lymphoid cells (T-cells) are transplanted into an immunosuppressed recipient incapable of rejecting the graft. The transplanted T-lymphocytes recognize histocompatibility antigens of host tissues as foreign, become sensitized, proliferate, and directly or through secondary mechanisms attack recipient tissue. The primary target organs of GVHD are the skin, gastrointestinal tract, and liver. GVHD can occur as a result of organ transplantation or bone marrow transplantation.
Two forms of GVHD, acute and chronic, have been described and differ in their onset and their clinical features. Acute GVHD (aGVHD) occurs in the first 100 days post-BMT, with the median day of onset being 19 days post-transplant. The target organs of aGVHD include the skin, gastrointestinal tract, and the liver. In contrast, chronic (cGVHD) presents a far more varied multiorgan “autoimmunity” clinical picture that includes liver dysfunction, pulmonary fibrosis, sclerodermatous skin changes, oral and gastrointestinal mucosa changes, and a reduced production of tears and saliva. The onset of cGVHD occurs between 100 and 400 days post-BMT. Because it involves many organs, cGVHD can cause significant morbidity and disability.
GVHD is an example of a general autoimmune disorder with oral involvement. Oral findings are seen in both acute and chronic GVHD. Oral involvement ranges between 33% and 75% for patients with aGVHD and up to about 80% for those with cGVHD. In some patients, oral symptoms are the most significant clinical finding of GVHD. Oral lesions in GVHD may be lichenoid or lupus-like in appearance. Oral findings of aGVHD include painful desquamative, erythematous, and ulcerative mucosal lesions [1,2]. In cGVHD, they are lichenoid with associated erythema and ulcerations; additionally, they may be associated with sicca syndrome characterized by xerostomia and progressive salivary gland atrophy [1,2,3]. Oral complications include pain due to the mucosal changes, altered or reduced taste, and may have a potential impact on speech, deglutition, and use of oral prostheses (when present). Oral infection, particularly due to candida species, and dental demineralization and caries may also occur.
The conventional management of oral cGVHD consists of systemic immunosuppressive therapies combined with proper oral hygiene and the judicious use of topical steroids [1,2]. However, for patients with oral cGVHD as the most significant clinical finding, the use of systemic immunosuppressants may result in immunosuppression of the host with attendant systemic complications. In addition, some patients experience considerable and refractory oral complications, even with maximum doses of systemic immunosuppressants.
Topical formulations of some immunosuppressants, such as cyclosporin A (“CsA”), have been used in the management of various autoimmune conditions [4,5]. U.S. Pat. No. 4,996,193 to Hewitt et al. discloses formulations for the topical application of CsA to skin tissue in the treatment of autoimmune diseases, T-cell mediated immune diseases, and inflammatory conditions. In addition, methods of use of these formulations, with or without accompanying systemic doses of CsA, are discussed. Topical formulations of CsA have also been employed in the management of oral cGVHD [4]. However, some GVHD patients do not respond well to systemic or topical formulations of CsA [4]. Furthermore, topical formulations of CsA are ineffective unless administered at relatively high concentrations. As a result, the high cost of CsA makes the use of these methods prohibitively expensive.
The generically available drug azathioprine (“AZA”) (brand name: Imuran) is one of the most widely used cytotoxic immunosuppressants in clinical medicine. AZA is a purine analog that is quickly metabolized in vivo to 6-mercaptopurine (6-MP), and thereafter to 6-thioguanine nucleotide (6-TNG). These compounds act as purine antagonists that interfere with the synthesis of DNA, RNA and protein [6]. They are known to act as immunomodulators, due to their selective effects on T cells and T cell-dependent responses [7] and their effects on natural killer cell activity [8] and humoral responsiveness [9]. AZA is commonly prescribed for many autoimmune diseases, including severe rheumatoid arthritis, systemic lupus erythmatosus, myasthenia gravis, autoimmune chronic active hepatitis, and pemphigus vulgaris [10,26]. In addition, AZA is commonly prescribed to inhibit the immune responses that cause rejection of organ transplants. The role of systemic AZA in the management and prevention of inflammatory bowel disease (IBD) has been well characterized [18,19], and AZA has been shown to be efficacious in the long term management of inflammatory bowel diseases, such as Crohn's disease, with less long term toxicity than that associated with corticosteroids [19]. Systemic AZA has proven effective as a steroid-sparing immunosuppressant in the management of chronic oral vesiculoerosive diseases, such as pemphigus vulgaris and lichen planus [10, 11, 12]. AZA has been shown to be stable as a compounded liquid (50 mg/ml solution retained at least 96% of the initial concentration for 60 days at 25° C.) [14], and further is much less expensive than other commonly used immunosuppressants, such as cyclosporin A.
Systemic AZA is usually administered either orally or intravenously. Oral administration is the preferred route in most cases, since the intravenous preparation is an extreme irritant. The dosage depends on the clinical requirements and the hematological tolerance of the patient, but is usually in the range of 1-4 mg/kg/day.
However, when administered systemically, AZA also induces a wide variety of significant side-effects. The side effects of systemic therapy with azathioprine [6] can be categorized as either allergic or non-allergic in nature. The allergic-type reactions appear to be dose-independent and may include the following symptoms: rash, fever, pancreatitis, arthralgias, malaise, nausea, and diarrhea. The non-allergic effects are thought to be dose-dependent and include leukopenia, thrombocytopenia, hepatitis, and infection. AZA is also thought to be a mutagen and a carcinogen [26]. In light of these significant adverse effects, dosing and toxicity monitoring (including a complete blood count and liver enzyme studies) are required to monitor the patient's therapy. Weekly complete blood counts are recommended for the first 8 weeks of systemic AZA treatment, and patients are monitored closely for any evidence of infection, unexpected bruising or bleeding, or other manifestations of bone marrow depression [26,27].
Recent pharmacokinetic studies of alternate formulations of azathioprine for treatment of inflammatory bowel disease (IBD) have been undertaken to provide methods of local drug delivery in the lower intestine with reduced bioavailability and resultant systemic toxicity. In one study, AZA was administered as a delayed-release oral capsule and showed improved ileocolonic delivery with dramatically reduced systemic bioavailability [20]. In another study, four different formulations of AZA were compared, including intravenous, oral, delayed-release oral, and rectal foam administration [21]. U.S. Pat. Nos. 5,691,343 and 5,905,081 to Sandborn disclose methods for treating IBD by topical administration of AZA, using, for example, either rectal administration by an enema or oral administration of delayed release unit dosage form.
There exist only sporadic reports of the use of topical AZA in oral diseases, such as aphthous stomatitis and parodontosis [14,15], and as immunosuppressive therapy in the prevention of corneal graft rejection [16,17]. To date, the effectiveness of topical routes of AZA administration is unclear. While topical AZA was reported to have some beneficial effect in the treatment of parodontosis [15], topical AZA was ineffective in the treatment of corneal graft rejections [16] and aphthous stomatitis [14]. Therefore, a need remains for an effective means to combat oral GVHD and other oral autoimmune diseases that does not implicate the serious side-effects encountered with conventional systemic AZA administration routes.